Subspace

Subspace is the space "in between" normal space. It is what a subspace tunnel, such as the ones made by the Wayfarer, is punched through.

Since most sapient brains are not equipped to process what happens in the sublayer, sense of time and visual perception tend to be unreliable to anyone except Sianat Pairs.

Subspace tunnelling became the best option when it came to getting from A to B as fast as possible once FTL (faster than light) travel was banned. It uses a fourth dimension, the sublayer, to make the distance between points in three-dimensional space as close as possible without having to warp the fabric of reality.

Subspace is also used by deepods and tugs as a way to make journeys faster. Those carry a pinhole drive that creates temporary tunnels and weaves in and out of subspace, so as not to damage the three-dimensional universe. Exactly how this works is unknown, as this again seems to be the knowledge of the Sianat alone.